Atomic mass
Atomic number
Number of electrons
Number of neutrons

Atomic number

Explanation:

For the chemical specie, Z is the atomic number of atom shown.

Usually with most elements;

                       ᵃₙX

 X is the symbol of the element

 a is the atomic mass or mass number

 n is the atomic number

In this problem, A is the atomic mass

                          Z is the atomic number

Atomic mass is the number of protons and neutrons

Atomic number is the number of protons.

f=ma newton

f=100x2.5=250n